In order to be able to transfer packets to and from remote devices, a communication device uses the Internet Protocol (IP) address of the destination to designate to where the packet should be transferred and its own IP address to indicate to the remote device where to send the reply packets, if any. As a result, each device is assigned an IP address when connecting to a network. The IP address comprises a network portion and host or device portion. The network portion is assigned according to the network to which the device is directly connected, and the host portion is a unique value within that local network.
In mobile networks, mobile devices are connected to an access network via a radio link with a base station. The base station provides a radio link for connecting with several mobile devices that are in its coverage area. The base station in turn is connected through an IP connection to an access network. The access network is connected via edge routers to the Internet, thus providing connectivity for the mobile devices to any device that is connected to the Internet.
Mobile devices are unique in the sense that when moving they may leave the coverage area of one base station and arrive in the coverage area of a different base station which may result in the mobile device being connected to a different local area network. The movement of the mobile device between base stations may result in a clash between the network address of the new local area network and the address part of the IP address of the mobile device. The clash should be resolved in order to maintain the ability of the mobile device to transmit and receive packets.
One solution for this clash is to assign a new IP address to the mobile device when it connects to a new base station where the network part of the new address is aligned with the new local area network address. This solution may be problematic in that changing the IP address of a mobile device in the middle of a session involves various complex operations to enable the continuation of established connections between the mobile device and other devices.
Another resolution of the clash may involve using Proxy Mobile IP protocol (PMIP) where the packets are tunneled between the base station and a Mobility Anchor Point (MAP) as the packets are transferred to and from the edge router and Internet. When a tunnel is created, a special IP address is used to transfer the packets between the MAP and the base-station through which the mobile device is connected. When the packets enter the tunnel, the packet is encapsulated with an additional IP header containing the tunnel IP address, and when the packet reaches the other endpoint of the tunnel, the extra header is removed (decapsulated). In this approach, the source and destination devices are able to communicate regardless of the actual base station being used by the mobile device. When the mobile device moves, a handover operation occurs between the original base station through which the mobile device had originally connected to the network and the new base station through which the device is currently connected to the network. The handover operation includes among other operations, the setting of a new tunnel between the MAP and the new base station for all traffic related to the IP address of the mobile device. The handover mechanism enables a mobile device to continue its communication without having to change its IP address. Moreover, this mechanism is transparent to the mobile device and to the peer devices with which the mobile device communicates with.
Utilization of a centralized MAP may introduce some limitations. First, all IP address allocations for all connecting mobile devices are performed by a single device, the MAP, which handles control traffic requesting a new IP address and the resulting reply between the base stations and the MAP. Second, all data traffic between the mobile devices and their destination devices in the Internet are routed through a single central device, the MAP. Third, all packets transferred to and from the base station are tunneled resulting in an increase of overhead bytes as a result of the encapsulation that takes place. Fourth, the MAP requires extra processing power to encapsulate and decapsulate all packets arriving from and to the base stations. Fifth, the need to route all traffic through the MAP may lead to non-optimized routs, for example, when both the source and destination devices are in the same access network. Although traffic could be routed directly between them, it is still routed through the MAP using tunnels between the MAP and each device.
It will be appreciated that for simplicity and/or clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, if considered appropriate, reference numerals have been repeated among the figures to indicate corresponding and/or analogous elements.